Press clutch to start issue

[CagaA4]

Hi All,

I had an issue with my clutch master cylinder that meant it needed replacing as it wouldn't start.

The workaround was to grab another one and connect it to the harness and push the rod down to test, which worked fine as expected.

I went ahead and replaced it and without bleeding tested the car started with the clutch pedal down, which it did.

I then fully bled it up and then now it won't start due to the push clutch to start message.

If I open the bleed valve and press the pedal to the floor, all good it starts. With the system fully bled, it won't start at all.

It's running a new clutch (sachs) that was installed by a garage a few months ago.

What am I missing?!

 

[CagaA4]

Ps, the old master cylinder after inspection has disintegrated, loads of plastic bits fell out into the return line, which I've cleared. The fluid is super clean and clear as it bleeds from the slave.

 

[spartacus 68]

Interesting read here. Eventually traced the error to the wiring that goes to the ECU. Not saying that is the scenario in this case. Check out the VAG specialist tools at the end of this thread! https://www.audiownersclub.com/forums/topic/19555-clutch-pedal-switch-for-engine-start-f194-fault/

What I would say is you need to get the car scanned to see if any error codes are logged. There's a clutch switch on the master cylinder from my understanding.

 

[CagaA4]

Yeah there's three position sensors actually, hall sensors.

I've read that it's a crap design and made worse when using aftermarket clutches.

The question is, how do I fix it if the clutch is new, master cylinder is new sensor works and clutch bled.

I've read people sleave and extend but surely there is a way of using an aftermarket clutch kit without bodging stuff either mechanically or electrically. Otherwise, how can companies like sachs sell them?!

Fit a sachs slave too?!

Confused...

 

[CagaA4]

I've now also installed as a punt the H revision master cylinder and pressure bled the clutch.

I still can't start the car as it thinks the clutch is up...

If I undo the bleed valve on the slave and press the lifeless clutch to the floor, it allows the pedal to travel further to the floor and the car starts fine. However when the bleed is closed, the travel of the pedal is reduced slightly and the car won't start.

 

[rum4mo]

@CagaA4, how did you resolve this finally, I'm having trouble starting my 2011 S4, I'm sure that you know now that pressing the clutch pedal down fully while there is air in the hydraulic line is allowing the hall effect switches to be enabled and so allow the engine to be started. While trying that with the hydraulic line fully bled ends up with the clutch slave cylinder reaching its physical end stop which is before the clutch master cylinder piston has managed to reach its correct end position - by which time it would have been able to enable the 3 switches and so enable engine starting.

 

[Simon]

There is a widely reported issue on audizine with aftermarket clutches on the b8 platform where the auto adjust mechanism doesn't work as well as a standard clutch leading to the push to start issue. I have the same issue at the moment when you really have to push the pedal into the floor to get the car to start, the recommended fix over there is a longer clutch rod and there is a guy that sells them.

I just bought a used clutch slave cylinder from ebay for £20, I've taken the rod out and cut it in half, put it through a 6mm die and used a threaded sleeve to rejoin it (with lots of locktite) and now just need to fit it to the car, the bonus is only the rod needs to be changed so I don't even need to bleed it after. All it needs is 7mm extension to work apparently.

 

[rum4mo]

Yes I think that I've revisited everything written on this, good to see that you threaded the rod and used a threaded joining piece to achieve the extra 4 > 6mm extra length. Strange but true, up until this evening I was considering becoming a good enough electric welder, and fabricate a sleeve and weld the rods into it - until tonight in my bath(!) I thought about doing what you have described.
I know that the guys across the pond use 1/4" which is just over 6mm, I was going to play safe and stick with 4mm>6mm and if necessary remove the rod and readjust it or swop with another one held as spare without any Loctite - if I sensed this was about to happen again.

Unfortunately, my S4 is in a local VW Group Indie getting its engine mountings replaced as the RHS one is leaking, I did ask them which brand of engine mountings they were going to fit as I had considered the 034motorsport solid ones, they said probably Lemforder and I replied that that was not an option for S4 - and I might have been dismissed, anyway, car went in Tuesday morning 07:30, I phoned them at 17:30, it now seems that they have found I was right wrt available correct engine mounts for S4, so it is still in the workshop! I only started getting "proper" stroppy about not being able to enable the starter the day before I handed it in - oh joy! If I'm being honest this has been a 1 in 10 engine starts for a couple of years or more - and I chose to ignore it and think it was just due to me wearing different shoes! If it ends up getting Audi engine mountings fitted that will hurt my wallet a lot, but if it needs that it gets that.
I'm going to just buy a new Febi clutch slave cylinder as I'd reckon that that current one will be nearly bust by the time I get it back and in my garage!

Thanks for suggesting/confirming threading and adjusting to size as an option, I hope it works fine for you!

Edit:- if I'm being honest, I don't mind swopping cylinders as I've never ever changed the fluid in the clutch fluid lines!

Another edit:- I just wonder if VW Group ever changed the length of this push rod when they evolved this slave cylinder through its life time, another reason for buying a new cylinder, I'll report after things come together!

 

[Simon]

It only seems to be an issue with aftermarket clutches - mine is a sachs 15% uprated one. Don't forget that the clutch shares fluid with the braking system so if that has been changed (it should have been at some point in the cars lifespan) then the clutch fluid by default will have been done too.

having had a nightmare with bleeding a BMW clutch slave cylinder I would do everything I could to not have to bleed the Audi one!

 

[rum4mo]

Oh don't worry about the brake fluid in my S4, it gets replaced by me every 2 years, same on all our other cars in the family, just the clutch that I've not bothered with due to them typically having a plastic cylinder assembly and a plastic bleed valve.

I agree that this issue will hit most people that fit uprated clutches, but it does affect all cars with Audi clutches, eventually, due I think, to the auto adjust on the clutch cover stopping adjusting, the release arm settling/partially collapsing and the release arm pivot changing shape a bit.

I was chatting to one of the owners of my local VW Group Indie today and it seems that most people just tack a blob of welding rod onto one end of the slave push rod.

I've ordered in a new correct model Febi slave cylinder via an ebay trader and so got 20% off with the current deals, so I'll see how it compares in length with the one in my car when that arrives.

Edit:- unfortunately I was asked if I could take my car back as Audi has let them down with delivery of the correct engine mountings for B8 S4! They will get back in touch with me when these mountings that are currently on back order with no fixed date of clearing that, are back in stock in the parts warehouse in UK!

 

[rum4mo]

@Simon, I've bought threaded sleeves and also a couple of different lengths of high tensile steel grub screws, I plan to use the grub screws as a "space filler" within the threaded sleeve - so if I just use Loctite instead of welding the rod<>sleeve ends, then as the threads in both cut parts of the push rod will be tightened and so there will be less clearance between the male and female threads, the Loctite will be able to set hard enough to provide a locking function - if you have just loosely screwed the rod parts into the threaded sleeve while covering them with Loctite then I'd doubt if the Loctite will ever set/harden enough to stop any further movement of these 2 push rod parts.

I'm just, as usual, going for overkill as I want this mod to work - and I've got plenty time as I'm waiting for threaded sleeves, grub screws and new slave cylinder to arrive - and my S4 continues to sleep in my garage!

 

[Simon]

I've got some low temp "Alumiweld" rod to put in mine to basically do exactly what you are talking about for the same reasons, I did think about dropping a ball bearing or two in there as an alternative.

 

[rum4mo]

I completed mod’ng the pushrod from the new Febi or maybe the Sachs slave cylinder, I used an M7 round threaded sleeve, 20mm or 25mm long and a suitable length M7 grub screw, ending up with a length increase of 5.5mm in the slave cylinder pushrod.
It took until the week before Christmas for Audi in Germany to replenish their stocks of the “AE” version of engine mounting, so along with an extra 2 days for my workshop to source a special tool needed, I only got my car back on Thursday!
@Simon, did you change your pushrod yet?

 

[Simon]

I haven't actually it is still sat on my desk waiting for some warmer weather to get under the car and fit it.

 

[Simon]

for the record I am not changing my slave cylinder I am just changing the rod, has it fixed your issue?

 

[rum4mo]

For various reasons, detailed on my postings to the "engine mountings" thread, I have not yet been under my car, plus in the few times that I've driven this car since I first posted about this "press clutch to start" issue, I've not had any repeat of not starting, but, once I've fitted the new bolts to the subframe and lower brace and steering column, I will look into this.

I have a new Sachs slave cylinder with the extended push rod in the boot - just in case, but I'll remove the existing original push rod, measure it and probably fit the extended one if the original push rod is the same length as the new one was originally. Maybe, just maybe, after doing that, I'll consider fitting an adjustable clutch pedal stop to protect the slave cylinder.

I'll probably even push some fluid out of the slave cylinder as it has never been done since the car was new, the rest of the fluid can wait until the warmer weather as it is due this year.

 

[Simon]

isn't the clutch fluid on the same circuit as the brakes?

 

[rum4mo]

isn't the clutch fluid on the same circuit as the brakes?

Oh yes, but other than slight movement/mixing between the clutch circuit, or "leg" and the brake circuit "legs" , the fluid in the clutch circuit or "leg" will just stay in there along with any particles of rubber from the primary and secondary clutch cylinder seals, so it is always a good plan to "dump" some fluid out of that circuit or "leg" as well as each of the brake circuit "legs". When you change the brake fluid you "dump" fluid out of each of the callipers in turn, then you should really do the same at the clutch secondary cylinder fluid valve.

 

[Simon]

Makes sense

 

[Hangn]

Audi B8/8.5 Extended Slave Cylinder (B8EXSLV) — JXB Performance

THE solution to the Push Clutch to Start issue that occurs in newer manual transmission Audis.

www.jxbperformance.com

 

[rum4mo]

Audi B8/8.5 Extended Slave Cylinder (B8EXSLV) — JXB Performance

THE solution to the Push Clutch to Start issue that occurs in newer manual transmission Audis.

www.jxbperformance.com

Oh yes, that was one way to solve this issue, I just took the DIYer route and made up an adjustable push rod - actually a lot like clutch push rods used to be maybe 30 or 40 years ago. This Audi/Porsche way of having a "smart" primary clutch cylinder has ended up being just too smart for their owners, good for the workshops though.

 

[Simon]

Audi B8/8.5 Extended Slave Cylinder (B8EXSLV) — JXB Performance

THE solution to the Push Clutch to Start issue that occurs in newer manual transmission Audis.

www.jxbperformance.com

This is the exact same solution as myself and Rum4mo have done, the guy started out by having the problem himself and then finding and selling the solution on Audizine.

If the price had been reasonable I would have just bought it from him, but $140 vs £3 for the hardware and some time I went the DIY route.